I have an AT&T SGH-I337. I successfully downgraded from NB1 to MK2, rooted, and installed SafeStrap. I had successfully booted to stock MK2 at this point.

I downloaded Deadly Venom Kitkat Magic Tool. I used SS to wipe all except external sd. Stock rom is active. Then queued 4 zips to install -> GE-SAFESTRAP-XXUFNBH-26.zip, GE-SLiM-F4ST-ADV-KK-26.zip, UPDATE-SuperSU-v1.93.zip, and AT&TNB1KernelModules.zip. I hit home -> reboot -> download. I used ODIN to flash AP, BL, and CP from Deadly Venom tool. I unchecked auto-reboot, flashed, hold power. Safestrap says 'Safestrap Disabled', then I get bootloop at the Samsung logo. Next I went back to download mode, tried to flash AP, BL, and CP again with auto-reboot enabled. Still stuck at Samsung logo.

I have an AT&T SGH-I337. I successfully downgraded from NB1 to MK2, rooted, and installed SafeStrap. I had successfully booted to stock MK2 at this point.

I downloaded Deadly Venom Kitkat Magic Tool. I used SS to wipe all except external sd. Stock rom is active. Then queued 4 zips to install -> GE-SAFESTRAP-XXUFNBH-26.zip, GE-SLiM-F4ST-ADV-KK-26.zip, UPDATE-SuperSU-v1.93.zip, and AT&TNB1KernelModules.zip. I hit home -> reboot -> download. I used ODIN to flash AP, BL, and CP from Deadly Venom tool. I unchecked auto-reboot, flashed, hold power. Safestrap says 'Safestrap Disabled', then I get bootloop at the Samsung logo. Next I went back to download mode, tried to flash AP, BL, and CP again with auto-reboot enabled. Still stuck at Samsung logo.

GE-SLiM-F4ST-ADV-KK-26.zip? An add-on to Golden eye? If that's the case, try flashing it without that add-on.

You are on the NB1 bootloader correct?
If that is the case all you need to do in order to flash the add-on is Odin the ap_mk2_normal.tar, flash the add-on, and then Odin back the NB1 files AP, BL, and CP.

I booted to download, flashed ap_mk2_normal.tar.md5 with auto reboot. Then I booted to safestrap, wiped all except external SD, flashed GE-SAFESTRAP-XXUFNBH-26.zip, UPDATE-SuperSU-v1.93.zip, and AT&TNB1KernelModules.zip in that order. Reboot back to download, flashed AP, BL, and CP from Deadly Venom tool with auto-reboot. Stuck again at Samsung logo.

Not sure if it's worth mentioning but I flashed the non-SafeStrap version of Goldeneye before now, realized my mistake, and started using the correct rom. Could it have flashed something that I need to revert?

Edit: I am current flashing the MK2 downgrade to try to boot so I can try to pick back up from a booting rom.

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